1. Field of the Invention
This invention relates to coating structures, and more particularly, to a photocatalytic film structure.
2. Background
Photocatalytic materials are bionic materials with self-cleaning functions, and therefore, they have now been widely used in daily life technologies. Advancement of technological developments and improvements of living standards in the recent years have drawn continuing increased attention on the safety of photocatalytic products, in addition to their effects (e.g., self-cleaning and antibacterial functions) associated daily use products.
Conventionally, photocatalytic coatings with polymeric resins, if being applied outdoors, might age in sunlight due to the presence of the polymeric resins. As such, the photocatalytic coatings cannot utilize the ultraviolet spectrum from sunlight to activate photocatalysis for achieving decontamination and deodorization.
On the other hand, as the photocatalytic coatings become rougher and have greater surface areas, the effect of photocatalysis is better. However, the photocatalytic ceramics prepared by sintering have surface atoms of the particles diffused towards the center thereof during sintering, such that the surfaces of photocatalytic coatings tend to be smooth. Hence, photocatalysis of the photocatalytic ceramics is ineffective.
Usually, the methods for immobilizing a photocatalytic material on a substrate include sol-gel methods, electrochemical deposition, chemical vapor deposition, hydrothermal methods, reaction evaporation, spraying methods, dipping, spin coating, and screen printing. For example, in a reactive evaporation, which is used to prepare a TiO2 photocatalytic material, polymeric agents such as adhesives are added to increase the adhesion between materials or the adhesion between a material and a substrate. In order to remove volatile agents, heating or sintering is sometimes used to remove residual volatile agents. Further, the solidification of an adhesive is accelerated to enhance the adhesion with the substrate to form a photocatalytic film.
However, the reactive evaporation usually results in residual acidic or alkaline solutions, which would cause body damage, food contamination or environmental hazards after long-term contacts. In addition, the production of a TiO2 photocatalytic film immobilized on a substrate is conducted by mainly using processes, such as immersion plating, sputtering, curtain plating, brush plating and spin plating. The adhesions of the TiO2 photocatalytic films to the substrates prepared by the above methods are poor, such that the films are easily peeled off upon the application of an external force.
A photocatalytic film produced by physical vapor deposition or chemical vapor deposition is relatively thin, i.e., about 1 micron or smaller. Ultraviolet rays might directly penetrate through the photocatalytic film, such that light scattering and absorption cannot take place uniformly on the film. The small overall surface area of the film makes the effect of its photocatalytic treatment of external organic contaminants poor. Moreover, since the photocatalytic film is too thin to sufficiently endure an outdoor environment (e.g., on outdoor walls or bridge surfaces) which abrades and harms the film in the long-term, the rapid erosion and disappearance of the film often happen at those areas, and thereby losing the original photocatalytic properties of the film.
Accordingly, the present disclosure provides a photocatalytic film structure which can resolve the above issues.